The Hidden Fee Disclosure Act of 2023 amends federal pension and health law (ERISA) to require greater transparency around fees charged by service providers to employer-sponsored health plans, particularly pharmacy benefit managers (PBMs) and third-party administrators (TPAs). The bill mandates detailed, itemized disclosure of compensation, rebates, discounts, and hidden fees that these providers receive, rather than allowing aggregate reporting, so plan sponsors can better understand true costs. It specifically targets PBM practices like spread pricing, clawbacks from pharmacies, and rebate arrangements with drug manufacturers, requiring annual reports within 60 days of each plan year detailing gross and net drug spending, pharmacy-owned revenue, and fee categories. Similarly, TPAs must disclose recovered overpayments, subrogation amounts, and other retained fees. This primarily affects employers offering group health plans, their employees and beneficiaries, and the insurance and pharmacy benefit industries; the Secretary of Labor must issue implementing regulations within one year of enactment, with the disclosure requirements taking effect January 1, 2025.